In today""s automotive market, there exist a variety of electric propulsion or drive technologies used to power vehicles. The technologies include electric traction drive systems utilizing batteries and/or fuel cells as an energy source, with a myriad of power converting technologies such as DC-DC converters, transformers, generators, and inverters used to provide electrical power at desired voltage and current levels and wave forms. An electric vehicle will require electrical sources at different voltage levels to operate different vehicle systems. For example, an electric traction motor will typically be operated at a high voltage level (200-450 volts), and accessory systems such as radios and door looks may be operated at a relatively low DC voltage (12-48 volts).
The plurality of voltage levels needed to operate an electric vehicle and its accessories require corresponding electrical converting equipment to transform the energy source in the vehicle to the desired voltage levels. In the past, multiple DC-DC converters have been used to provide low voltage DC power to power vehicle accessories. This plurality of electrical converting components adds cost and complexity to a vehicle. Thus, there is a need in the art of electrical vehicles to provide a simple cost-effective method for providing multiple voltage levels in an electric vehicle.
The present invention includes a method and apparatus to provide power to an electric traction motor in a vehicle and also to provide secondary low voltage for vehicle accessories. The present invention utilizes an electric traction motor having dual windings providing electrical energy/power to drive the electric traction motor and also providing a low voltage DC source for vehicle accessories. The electric traction motor is electrically coupled to an inverter that supplies time-varying current to a primary winding electric traction motor to electromagnetically vary the torque of the electric traction motor. A battery or fuel cell with a DC-DC converter provides a high voltage DC bus that is chopped by the inverter into the time-varying current.
A secondary winding included in the electric motor is electromagnetically coupled to the primary winding and time-varying current supplied by the inverter. The secondary winding has a turn ratio that allows the voltage supplied by the secondary winding to be less than that supplied by the primary winding. The output voltage of the secondary winding is then applied to a rectifier to be rectified into a DC voltage that may be used by vehicle accessories. As described previously, vehicle accessories typically operate on DC voltages in the range of 12 to 48 volts. The voltage supplied by the secondary winding will vary as the time-varying current applied by the inverter to the motor is changed to control the torque of the electric traction motor. To compensate for this voltage variation, the rectifier includes a bank of switching elements that is controlled in closed loop fashion to supply a desired voltage. In this manner, the DC voltage generated by the secondary winding and rectifier can be controlled in most cases regardless of the magnitude of the time-varying current applied to the primary windings of the electric traction motor. In operating conditions where the time-varying current supplied by the inverter to drive the electric motor drops below the necessary level to sustain the desired DC voltage output of the rectifier, a high frequency output generated by the inverter will provide the electrical energy necessary for the secondary winding and rectifier to generate the desired DC voltage.
The dual winding and controlled rectification of the electric traction motor of the present invention is a low cost, highly reliable solution to the problem of providing different voltage sources or levels in an electric vehicle.